Abstract 208: Defining the functions of mitochondrial Telomerase Reverse Transcriptase

Over the last few years it has become clear that mitochondria are not only the powerhouses of the cells, having their sole function in producing ATP. Proteome-analyses of mitochondria from different organisms and organs revealed that more than 1000 proteins are localized in and or on the mitochondria. This by far exceeds the number of proteins required for classical mitochondrial functions, e.g. the respiratory chain, the tricarboxylic acid cycle, fatty acid oxidation and apoptosis. This suggests that many of these proteins have other, as yet unknown functions. We identified Telomerase Reverse Transcriptase (TERT), an enzyme that, in the nucleus, protects telomeres, the ends of the chromosomes, against shortening, also in the mitochondria. However, up to now only (TERT) deficient cells and mice or TERT overexpressing cells were used to study nuclear and mitochondrial functions of TERT. In this context, we demonstrated that reduction of endogenous TERT leads to increased reactive oxygen species (ROS) production in the cytosol as well as in the mitochondria. To analyze now specifically the functions of mitochondrial TERT, we isolated TERT deficient fibroblasts and transduced them with lentiviruses containing mitochondrially targeted TERT. We first validated these newly generated cells for transgene insertion and expression. Next, we analyzed compartment specific ROS production and apoptosis in the cells. We observed a reduction specifically in the levels of mitochondrial, but not cytosolic ROS. Moreover, apoptosis induction was significantly reduced in these cells compared to TERT deficient cells as well as cells containing endogenous TERT. Thus, mitochondrial TERT specifically reduces mitochondrially produced ROS and protects cells against apoptosis. In comparison to nuclear TERT, which has the main function to prolong telomeres, mitochondrial TERT specifically protects mitochondria from damage. Currently, we are creating mice that carry mitochondrially targeted TERT on an otherwise TERT deficient background for in vivo experiments.